The long term goal of this research is a better understanding of the processes which control bone resorption and bone accretion in vivo. Such an understanding is essential for the isolation and definition of the metabolic defects which cause bone disease. The specific aims are: (1) To test if the synthetic 1-34 fragment of bovine parathyroid hormone (PTH) causes changes in bone blood flow similar to those observed in experiments with PTH (Wilson). (2) To determine if experimental changes of bone blood flow cause changes in the release of calcium and inorganic phosphate from bone. (3) To investigate if the rapid effects of parathyroid hormone on bone are mediated by extraosseous sites and/or substances. (4) To study the mechanisms which initiate and maintain long term bone resorption and accretion. (5) To elucidate the regulation of bone blood flow. (6) To investigate if calcitonin plays a role in the control of bone blood flow. Avian species and particularly laying hens will be used for this project because of their rapid skeletal metabolism and because they have distinct periods when either bone resorption or accretion predominates. Methods to be used include: controlled perfusion of the isolated lower leg, measurement of the distribution of cardiac output with labeled microspheres and localization of H3-uridine and H3-thymidine in bone cells by autoradiography.